Taxonomy of seasonal and diurnal clear-sky climatology of surface urban heat island dynamics across global cities
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Knowledge of the temporally continuous dynamics of seasonal and diurnal surface urban heat islands (SUHIs) as well as their underlying determinants is crucial to better understand their variations at multiple time scales. Owing to the orbital limitation of satellites, previous studies primarily focused on SUHI dynamics at limited time nodes, either in a diurnal or seasonal cycle. However, a joint investigation of the continuous dynamics of seasonal and diurnal SUHIs (hereafter referred to as SUHIsea and SUHIdiu) remains lacking. The comprehensive taxonomy of the patterns of continuous SUHIsea and SUHI(diu & nbsp;)dynamics across global cities is also not clear. Using satellite-derived land surface temperature (LST) data, we investigated the prevalent patterns of continuous SUHIsea and SUHIsea dynamics across global cities by combining annual and diurnal temperature cycle models and the k-means clustering algorithm. Our results showed that: (1) Both SUHIsea and SUHIdiu dynamics exhibited six typical patterns including, single-peak type (SPT), single-valley type (SVT), peak-valley type (PVT), valley-peak type (VPT), two-peak type (TPT), and two-valley type (TVT). (2) The daytime SUHIsea dynamics pattern was closely related to the background climate, with SPT and PVT mainly occurring in cities located in the warm temperate and snow zones, SVT and VPT in the arid zone, and TPT and TVT in the equatorial zone. In contrast, the nighttime SUHIsea dynamics pattern depended more on rural land cover type, with SPT, PVT, and TPT mostly occurring in cities surrounded by barren lands with high albedo and SVT, VPT, and TVT in cities surrounded by dense vegetation with low albedo. We also find a significant negative relationship between daytime SUHIsea dynamics and urban-rural contrast in vegetation and between nighttime SUHIsea dynamics and urban-rural contrast in albedo across cities. (3) For SUHIdiu dynamics, SPT, PVT, and TVT were mainly located in cities with higher vegetation coverage in rural than in urban areas, while SVT, VPT, and TPT were in cities with higher vegetation coverage in urban areas. The SUHIdiu dynamics were found to be synthetically affected by the urban rural contrast in vegetation and albedo. We consider these findings to be beneficial for deepening the understanding of SUHI dynamics at various time scales.